Although applicable, in principle, to a multitude of micromechanical components, the exemplary embodiments and/or exemplary methods of the present invention, as well as the problem forming the basis of it, are explained with the aid of capacitive pressure sensors.
The starting point for explaining the problem providing the basis of the exemplary embodiments and/or exemplary methods of the present invention is a capacitive pressure sensor in which the capacitance of a first electrode, which may be elastically deflected by applying pressure, and the capacitance of a rigid second electrode, which is set apart and electrically insulated from the first electrode, are evaluated as an electrode pair.
Capacitive surface-micromechanics pressure sensors that are structured such that sacrificial layers underneath a diaphragm are removed through holes in the diaphragm or through lateral accesses under the diaphragm, the diaphragm forming the first elastically deflectable electrode, are generally known. Afterwards, the holes must be closed again, and additionally they have a negative effect on the stability and imperviousness of the diaphragm. Furthermore, it is known that a silicon diaphragm is used, it is made up of polycrystalline silicon. This is expedient in as much as the diaphragm electrode may only be made up of polysilicon or of a polycrystalline epitaxy-silicon layer that uses polysilicon as a starting layer due to the electric insulation of the two electrodes. However, in comparison with monocrystalline silicon, polycrystalline silicon has significantly worse electric and mechanical properties.
German patent documents DE 10 2004 036 032 A1, DE 10 2004 036 035 A1 and DE 100 32 579 A1 discuss a method for producing a micromechanical component, in particular, a diaphragm sensor, a self-supporting monocrystalline n-doped silicon lattice being provided on a p-doped semiconductor substrate, under which lattice a cavity is formed by selective dissolution or by rearranging porosified substrate material in high-temperature steps. A diaphragm of monocrystalline silicon, which is formed with the aid of an epitaxy method, is situated above the monocrystalline n-doped silicon lattice.
FIG. 6 shows a schematic sectional view of a capacitive pressure sensor to explain the structure of a micromechanical component in the form of a capacitive pressure sensor to explain the problem providing the basis of the exemplary embodiments and/or exemplary methods of the present invention.
In FIG. 6, reference numeral 1 labels a p-doped silicon semiconductor substrate, above which is formed a self-supporting monocrystalline n-doped silicon lattice 3 along with a cavity 2 situated below it, in accordance with the teaching of DE 10 2004 036 032 A1 and DE 10 2004 036 035 A1. A monocrystalline, epitaxially deposited silicon layer 4 having a diaphragm region 4a, which acts as first elastically deflectable electrode region E1 of the micromechanical capacitive pressure sensor, is situated above n-doped silicon lattice 3. A peripheral region 4b of monocrystalline, epitaxially deposited silicon layer 4, which acts as first connection region A1 of the micromechanical capacitive pressure sensor, is provided to the side.
An insulating sacrificial layer 5, which is made up of silicon oxide, for example, is deposited and patterned on the monocrystalline silicon layer 4 using known methods. Monocrystalline silicon layer 4, in particular, its peripheral region 4b and thus also silicon substrate 1 situated under it, may be electrically contacted via one or more openings O formed in sacrificial layer 5. This occurs in that after one or multiple openings O is/are formed, a polycrystalline epitaxial silicon layer 6 is deposited on sacrificial layer 5. In the region of openings O, epitaxial silicon layer 6 may be implemented both as polycrystalline and monocrystalline, depending on the starting layer used.
Polycrystalline silicon layer 6 is now patterned using a photolithographic technology, followed by a trench-etching step for forming traversing trenches 6a, such that an electric separation of second electrode region E2 and of second connection region A2 may be achieved. One or more self-supporting elements 6b of polycrystalline epitaxial silicon layer 6, which form second connection region A2, are thus electrically connected to first connection region A1 of monocrystalline silicon layer 4 and are used to contact it from outside. Furthermore, trenches 6a are used to generate a perforation in second electrode region E2, through which sacrificial layer 5 between first monocrystalline silicon layer 4 and second polycrystalline silicon layer 6 may be removed using sacrificial-layer etching (e.g., gas-phase etching). In this manner, a monocrystalline first electrode region E1 is obtained whose deflection with regard to second electrode region E2 may be evaluated capacitively.
Afterward, the depositing and patterning of a metallization level 7 takes place, on which contacting surfaces 7a, 7b are formed, via which second electrode region E2 and second connection region A2, respectively, may be connected to corresponding connections of a housing (not shown) by wire bonding. However, the relatively high stray capacitances of substrate 1 and of monocrystalline silicon layer 4 with regard to the (not shown) housing are a disadvantage of such a structure.